This invention relates to an air-cushion vehicle in which pressurized air is blown from an engine-driven propeller mounted in the hull against a pressure-receiving surface formed by a ground surface, ice surface, snow surface, or water surface, for example, (hereafter referred to pressure-receiving surface) in order for the vehicle to be levitated and ride on a cushion of air across land, water, ice, snow, marshlands, etc.
Air cushion vehicles, or hovercrafts, are known in the art, and include a hull which supports an engine-driven fan. A skirt extends downwardly from the bottom side of the hull to the surface and encloses a cushion of air. The skirt is formed by a series of finger skirts located around the periphery of the hull. The air from the fan flows into the enclosure and the finger skirts and thus forms the air cushion.
FIGS. 6 through 10 show the construction of a finger skirt in accordance with the prior art. Each finger skirt is an independent collapsible bag which is mounted so that the bottom of the skirt is slanted toward the hull. In FIG. 6, the pressurized air for the levitation of the hull flows into a finger skirt 20 through the two open sides (formed between the points 34, 31, 35, 36, 37 and 38) which face the hull in order to inflate the finger skirt, and then the air flows out through a gap between the pressure-receiving surface 22 beneath the hull 21 and an edge of the skirt which is formed between the points 36 and 37.
Finger skirts are usually fabricated of a flexible material, and, when they are inflated by the pressurized air, they have a tendency to change to an overall rounded shape; however, because the side faces are restricted by the adjacent finger skirts, only the outward face formed by points 32, 33, 37, and 36 changes to a semicylindrical shape as shown in FIG. 10.
Because the attachment of the skirts to the hull is done in such a manner that the bottom of each skirt is slanted toward the hull, the bottom of each inflated skirt is such that point a (shown in FIGS. 8 to 10) is in contact with the pressure-receiving surface 22, and point b, which is the bottom end of the vertical boundary surface with an adjacent skirt, is positioned higher than point a. This is true because the line between the points 36 and 37 becomes arcuate or rounded due to the air pressure, as shown in FIG. 10, and only a short portion (point a) at the center of the line between points 36 and 37 is adjacent the surface 22.
Thus, when the hull is riding on the cushion of air, the pressurized air for the levitation of the hull leaks out through the triangular shaped gaps between the centers of two adjacent finger skirts, of which point b is the vertex. This leakage results in an increase in the amount of force required for levitation, and consequently also in accompanying increases in the sizes of the engine-driven propeller and various ducts, and in the size and weight of the hull itself. Although one method used to counteract this drawback is to reduce the width of the finger skirts in order to reduce the size of the triangular gaps, this results in an increase in the number of skirts, which presents an economic problem economically.